Synthesis and Solid‐State Investigations of Oligo‐Phenylene–Ethynylene Structures with Halide End‐Groups

Abstract

In the field of material science functionalization of substrate surfaces (e.g. metal, graphite) with organic molecules is of increasing interest. Desirable targets are molecules with functional groups providing for two‐dimensional assembly and three‐dimensional crystal growth. We have synthesized a series of halogen‐end‐capped oligo‐phenylene‐ethynylenes (OPEs) to study the interactions at the solid/liquid interface and in crystal structures. Organohalides can be involved in a wide variety of intermolecular interactions such as C–X···H, C–X···X–C and C–X···π‐orbitals. The range of halogen‐based interactions and the diversity of intermolecular forces along different crystal axes makes the investigation of such structures particular interesting and challenging. Here we probe the interplay of halide end‐groups and the backbone of an OPE to investigate the intermolecular interactions in both solution depositions (2D) and X‐ray crystal structures (3D). The STM images and the crystal structures of each OPE reveal striking packing similarities. For each molecule, a plane in the crystal structure with an arrangement of molecules resembling its two‐dimensional packing on a flat surface was found. These results support the hypothesis of sheet‐by‐sheet crystal growth and suggest that flat surfaces would be ideal interfaces to promote crystal growth for halide‐end‐capped OPEs.

The Halogen Bond

“…Electrophilic halogens have formed halogen-bonded crystalline complexes with a variety of π-systems, for instance, double or triple bonds , (Figure ) and aromatic (Figure ) moieties . Adducts in the solid state are similar to those formed in solution, and these latter systems are of particular relevance as they are prereactive states in addition reaction to olefins , and substitution reactions of aromatics .…”

Self-assembly of pyrene derivatives on Au(111): substituent effects on intermolecular interactions

“…9b So far, however, only a few more studies investigated the influence of the chemical nature of the halogen substituents on the surface-supported self-assembly process. [10][11][12][13] It has been recognised that for the construction of such 2D structures, halogen substituents may play the determining role in the structural formation by balancing the delicate interplay between molecule-molecule and molecule-substrate interactions. Therefore, an in-depth understanding of the effects of halogen substituents on the resulting intermolecular interactions is of utmost importance for the usage of X-bonds for the construction of molecular devices.…”

Nanopatterning by Molecular Self-assembly on Surfaces

“…It was also possible to design and synthesize halide end-capped oligo-phenyl-ethynylene (OPE) rods and compare their 3D crystal structure to their 2D arrangement on surfaces. [44] Currently we are working to combine such phenylacetylene architectures with a porous network to investigate template effects and even the dynamics of molecular motion at the interface.…”